The present disclosure relates to an earphone and an acoustic transducer and, in particular, those using a balanced armature unit.
An example of an acoustic transducer for use in an earphone and others is a so-called balanced armature unit as described in U.S. Pat. No. 6,751,326.
An example of an outer view of the balanced armature unit is depicted in FIG. 10. In this balanced armature unit, a yoke, a coil, an armature, and a diaphragm are accommodated in an accommodation casing 100 with a predetermined arrangement. With a driving current flowing through the coil, the armature is vibrated. That vibration is transferred to the diaphragm to produce sound.
In this balanced armature unit, a funnel-shaped member 101 is integrally mounted on the accommodation casing 100. This member 101 has a sound output hole 101a. 
The sound obtained by the inner diaphragm is outputted from the sound output hole 101a of the member 101 to the outside of the unit.
This balanced armature unit is mounted inside of an earphone. In this case, in order to guide sound to an earpiece part to be inserted in an ear hole of a user, a sound path in an earphone casing and the member 101 are coupled together with a tube.